Because in almost all cases, it brings up an old dispute that wasn't resolvable in the first place, and that certainly isn't resolvable now.
Then let's just not have an open discussion forum. Have a forum involving only pre-approved letters that are judged based on novelty and what they add to the subject. In real life, the same subject come up over and over again. That's life, frankly. If the moderator doesn't care, butt out.